Heretofore, a honeycomb structure which is made of cordierite and onto which a catalyst is loaded has been used in treatment of harmful substances in an exhaust gas discharged from a car engine. Moreover, it is also known that a honeycomb structure formed by a sintered silicon carbide body is used in purification of the exhaust gas (e.g., see Patent Document 1).
When the exhaust gas is treated by the catalyst loaded onto the honeycomb structure, it is necessary to raise a temperature of the catalyst to a predetermined temperature. However, at the start of the engine, the catalyst temperature is low, and hence there has been the problem that the exhaust gas is not sufficiently purified.
Therefore, a method has been investigated in which a heater made of a metal is disposed on an upstream side of a honeycomb structure loaded with a catalyst, to raise a temperature of the exhaust gas (e.g., see Patent Document 2).
Moreover, it has been disclosed that a honeycomb structure made of a conductive ceramic material and provided with electrodes at both ends thereof is used as a catalyst carrier with a heater (e.g., see Patent Document 3).